“Trench isolation” is known as a technique for separating from one another the devices of semiconductor equipment formed by integrating a large number of devices at a high density. The trench isolation structure is mainly constructed by forming trenches in a silicon substrate by dry etching, filling the trenches with SiO2 and planarizing a surface over the trenches by chemical mechanical polishing (CMP) in the end. This trench isolation has no increase in isolation size caused by a process such as the bird's beak process as compared with an isolation formed by LOCOS (Local Oxidation of Silicon). Therefore, it is suitable for the high integration of devices.
The above trench isolation structure is generally constructed by, for example, the method described in “First Semiconductor Process” (written by Kazuo Maeda, Kogyo Chosakai Publishing Co., Ltd., pp. 166-173, 2001). In the commonly used method of forming a trench isolation, for example, a silicon dioxide (SiO2) film and a silicon nitride (Si3N4) film as an oxidation mask are first formed on the top surface of a silicon substrate by chemical vapor deposition (CVD).
Then, an etching mask having a trench pattern is formed from a resist on the top surface of the silicon nitride film by ordinary photolithography, and trenches are formed in the silicon substrate through the silicon nitride film and the silicon oxide film by anisotropic etching such as reactive ion etching. Thereafter, a silicon oxide film is formed on the inner wall of each trench by thermal oxidation or chemical vapor deposition, and then a silicon oxide deposition layer is formed on the inside of each trench and the top surface of the silicon nitride film by, for example, chemical vapor deposition. The fillers are planarized by chemical mechanical polishing to form a trench isolation.
However, in the trench isolation formed by the above method, even if an insulator made of silicon dioxide is formed in each trench by chemical vapor deposition having relatively high coverage, when the aspect ratio (trench depth/trench width) of the trench becomes not less than 1, a local void is formed in the inside of the formed silicon dioxide. Therefore, when a heat treatment step is carried out after that, the formed void may expand and destroy the trench isolation.
Then, to form a silicon dioxide deposition layer having few local voids, chemical vapor deposition in which a mixed gas of ozone and tetraethoxysilane (TEOS) is used as a reactive gas is employed. However, even in this method, a local void is formed in the silicon dioxide deposition layer formed in the inside of a trench having an aspect ratio of not less than 2. Since the silicon dioxide deposition layer formed by this chemical vapor deposition process has a lower density than that of a silicon dioxide deposition layer formed by another chemical vapor deposition process, it is difficult to form a silicon dioxide insulator having high resistance.
Further, an expensive vacuum apparatus is required in all the above methods, thereby boosting costs. In addition, since the raw material is gaseous, the methods have problems to be solved, such as the contamination of the apparatus and low production yield due to the generation of foreign matter.
Recently, a method in which a high-molecular weight liquid dihydrosilicon polymer is used as a coating type silicon dioxide precursor has been proposed (refer to JP-A 2007-45859). In this technology, a liquid product which is the distillation residue obtained by removing a low-boiling point component from the hydrolytic condensate of H2SiCl2 or a high molecular weight liquid product obtained by oxidizing and branching the hydrolytic condensate of H2SiCl2 with an inorganic acid is used as a silicon dioxide precursor. JP-A 2007-45859 teaches that, when a super high molecular weight silicon dioxide precursor having a weight average molecular weight of more than 500,000 is used in an Example, a good result is obtained. However, when the aspect ratio of a trench formed in the substrate is large, it is difficult to fill the trench with a coating type composition containing the super high molecular weight substance by coating, whereby a local void is readily formed as well.